Isobutanol can be formed from the fermentation of sugars which can be formed via the breakdown of cellulose. For example, solutions of up to approximately 2% by weight isobutanol in microbial growth have been produced in certain fermentation processes (Fraces Arnold, “The Race for New Biofuels,” Engineering & Science, No. 2, 2008). U.S. Patent Application Publication No. 20070092957 describes fermentatively producing isobutanol using recombinant microorganisms.
As microbes are further developed to withstand higher concentrations of isobutanol, it can be envisioned that isobutanol may compete with ethanol as a potential—fuel component or chemical feedstock derived from renewable resources. Unfortunately, there exist concerns regarding direct blending of isobutanol and other higher alcohols into the gasoline pool due to odor and automotive component compatibility issues. For this reason, there is interest in conversion of light alcohols into more typical petrochemical feedstocks for conversion into fuels or other valuable end products.
U.S. Patent Application Publication Nos. 20090099401, 20090030239, 2008013274, 20080045754, 20080015395, 20080234523, and others, each filed by E.I. Dupont de Nemours and Company, Wilmington, Del., are directed to the conversion of bio-derived isobutanol to butenes and isooctenes, among other end products. Each of these processes react isobutanol over a homogeneous or heterogeneous acid catalyst to form the desired reaction product, either a butene or an isooctene (diisobutylene).
Unlike tertiary butanol, which can be readily converted via dehydration into its constituent isobutylene and then into fuel blend components, such as diisobutylene, as disclosed in U.S. Pat. No. 6,936,742, the conversion of other light alcohols often requires higher activity catalysts and more severe process conditions. Significant recycle rates may also be required to result in acceptable conversion levels. Additionally, with bio-derived alcohols, water may be present with the feed, and separation is often difficult due to the components having closer relative volatilities and potential for forming various azeotropes.
Accordingly, there exists a need for processes for the conversion of light alcohols such as isobutanol into useful petrochemical feedstocks.